Radio navigational system



June 6, 1950 C. E. STRONG ET AL RADIQ NAVIGATIONAL SYSTEM Filed Sept.10, 1945 `3 Sheets-Sheet 1 .W mww l; Q

June 6, 1950 c. E. STRONG ETAL RADIO NAVIGATIONAL SYSTEM 3 Sheets-Sheet2 Filed Sept. 10, 1945 l n Uenior Cxmwas Eme. Smoncl Laws SmmHeavaN-nsmw,

Aitor y June 6, 1950 c. E. STRONG ET Al..

RADIO NAVIGATIONAL SYSTEM 3 Sheets-Sheet 3 Filed Sept. 10, 1945 InuenlorCmaauss.4 Em@ Smwo,

Lm. .Icom )mman-Mmmm@ By Aitor y Patented June 6, 1950 RADIONAVIGATIONAL SYSTEM ration of Delaware Application September 10, 1945,Serial No. 615,430 In Great Britain August 18, 19.44

(ci. 34e- 107) 4 Claims- The present invention relates to radionavigational systems in general, for example, systems lfor defining anapproach path, a glide path, or marker beacons, and `it has. for itsobject to provide radio navigational systems in which all the beacons atan aerodrome or airport or marine harbour1 for example, and locatedsubstantially at the same radiation center as regards Ia re. ceiver mayutilise the same .carrier frequency, and further to provide one or morecommunication channels for speech ,or other intelligence bearing signalWaves between the beacon Logittion and mobile receivers utilising thebeacons, also on the same carrier frequency as the beacon transmissions.

According to a broad aspect of the present invention a radionavigational system is characterised in that the radiation from a beaconcomprises a series of electrical pulses of. con-Stent pulse repetitionperiod.

Such a system enables the same carrier frequency to be employed vfor allthe beacons and any communication channels that may be required at thesame location.

According to one feature of the invention, the same pulse repetitionfrequency may be employed for all the beacons and channels, the pulsesof the respective beacons and communication channels, being time phasedwith respect to each other.

According to another -feature of the invention diierent pulse repetitionfrequencies may be used for respective channels.

Hereinafter, the various navigational beacons and communication channelswill be referred to generally as channels.

In such a system embodying the rst mentioned feature of the invention,the .channels are arranged to be normally quiescent and .are by:clically and successively brought into action by a pulse distributorsystem much in the .same `way as a .distributor system in a multiplexpulse `communication system. .A suitable distributor may be, forexample, a .delay network A.comprising a :four terminal passivetransmission network or artificial line which retards the passage of anelectrical current propagated therethrough and .consists of a plurality.of series connected ,cells made up of electrical impedances. The pulsesfor rendering the respective channels operative are `obtained bytappings .at diierent points along 'the articial line.

The mobile receiver for vexample on the aircraft utilising the channelsystem is then provided with a Ydistributor'which `is synchronised tothe transmitter distributor and directs the pulses received, to theirrespective receiving @Peritos in which they are .dealt with according iothe functions oi the respectivo channels.-

A radio navigational System according to .the invention possesses allthe advantages of oemig pulse technique and ,in addition tho bcaoochannels themselves may be used for crnmuni- .cation of speech or other.Signale 4for cram-P1@ .call Sien transmission by time ,modulating the.pulses cf the beacon channels provided that the time .duration of a sulc docs. not exceed the e1- lottcd time for the channel. For example thepulses of Va channel may bc duration modulated or time phase modulatedWithin .the .limito Qf thc .allotted channel period 1o accordance withthe amplitude of thc intelligence ssoaI -Wavc- Furthermore when thepulse is transmitted as e short train of carrier Waves, thc Carr-iol'may bo frequency .or phase modulated 11.1 .accordance with the amplitudeof the intelligence Seaal wave to be transmitted. Fort-hcc, amplitudemodulation by a signal Wave may be imposed upon one or more oi thebeacon channels A communication chan-ncl proper may be employed forcommunication of .continuous renee indice- .tions .to the aircraft.

The azimuth or approach path beacon and the `.confununi.cation channelshave a Working range of, for example, .50 miles to aircraft living10,000 :feet or over and the glide path beacon has, for example, a rangeof l() miles.

The signals of a channel, e. g. a communication channel can be relayed`from the aircraft receiver and can be used in lnown manner by an`voperator at the ,ground station for the meaS- urement of the range ofthe aircraft on` the ap.- Ypreach path. .The .range indications than betransmitted back to the aircraft by a com:- munication channel bytelephony `or by a method giving `direct range reading :n the aircraft.

continuous range is communicated ,as part of the airport or aerodrornemarshal-ling ar.- rangements 'then .only one marker beacon need beprovided, namely :the inner marker beacon. When such continuous rangecommunie tion is not employed an outer marker-beacon will also beprovided.

It `v/ill be observed that in a navigational sys,- tem embodying thepresent fin-Mention .and usine the distributor system referred to above,the call sign transmission does not interrupt vthe ap..- proach signalswhich is a necessary .condition in a system ,designed to remain gin.operation up :to

touch down vor beyond, and `further the indications are displayed in theaircraft which is practically a pre-requisite to automatic ying control.It will further be observed that the receiver main automatic volumecontrol may be operated from an omnidirectional communication channel.Therefore the course beacon can be given a high forward directivity andfails or false courses behind the antenna system would be masked.

Any known types of antenna systems may be The omni-directionalsupplementary radiation may be utilised as a communication channel, forexample, for telephone communication in accordance with known pulsemodulation technique, between the ground station and the mobilereceiver.

The invention will be further described in the following description ofsome embodiments employed sfor the respective ybeacons and may transmitthe same or different wave polarisations.

Furthermore, at the receiver suitable antennae for receiving differentpolarisations, for example horizontal and vertical antennae maybe used,the antennae being connected through mixer valves or other separatingdevices in the radio receiver in accordance with well known technique. l

In the case of an approach path beacon by which the path is dened by twooverlapping lobes, the lobes may be commutated in dot-dash rhythm aboutthe desired path, or the lobes may be stationary and modulated withdifferent respective distinguishing frequencies.

A beacon system for defining a glide path may be of any known type.

In the case of a system for defining a path by two radio beams arrangedto overlap in space, the said path being dened by constant ratio ofsignal strengths of the signals received from said beams, a single pathonly is usually necessary and it is then desirable to utilise thegreatest amount of the energy radiated from the transmitter for thatpurpose and to direct the energy into a single directive lobe. When anattempt is made to effect this concentration of power, a plurality ofsmall lobes appear in the radiation distribution diagram in addition tothe main lobe directed along the desired direction and these small lobesproduce false courses. By

good design of the antenna system it is possible.

to make these unwanted lobes very small and the signals therefrom veryweak. However, if the receiver approaches the antenna system from therear (as regards the main lobes) it will receive these small signals atfull strength when not too far from the antenna system on account of theautomatic volume control action in the receiver which enables thereceiver to attain maximum sensitivity if the signals are weak'. Even ifthe antenna system has no backward radiation false courses could stillbe obtained by reflection of the radiated waves from objects fallingwithin the main radiation lobes. This reflection would be weak but quitestrong enough to be picked up by a receiver as sensitive as would berequired to receive the main radiation at the maximum distance.

In order to eliminate these false courses, it has been proposed totransmit an omni-directional supplementary radiation which is receivedby the mobile receiver and utilised to control the gain of said receiveras regards reception of the main radiation as to reduce said gain whenthe field strength at the receiver of the supplementary radiationexceeds a predetermined value.

In such a system embodying the present invention, the supplementaryomni-directional radiation consists of a pulse modulated transmission.Further the main transmission producing the overlapping lobes to denethe desired path may also be pulse modulated.v

.thereof and taken in conjunction with the accompanying drawings inwhich Figure 1 illustrates in block schematic form the transmittingbeacons of a radio navigational system.

Figure 2 is an explanatory diagram used in the description of Figure 1.

Figure 3 illustrates in block schematic form a receiver for use with thebeacons as shown in Figure 1.

Figure 4 shows a detail unit of Figure 3.

Figure 5 shows in block schematic form another form of transmittingbeacon system.

Figure 6 is an explanatory diagram used in the description of Figure 5and Figure 7 shows in block schematic form a receiver for use with thebeacons as shown in Fig-1 ure 5.

Referring now to Figure 1, it will be assumed that all the channels (i.e. beacons and communication channels) are transmitted on the samecarrier frequency and that all channels have the same pulse repetitionfrequency, the pulses for the respective channels being time phased withrespect to each other. Y

In Figure 1 block I represents a square wave generator producing pulsesof Yrectangular wave form at a repetition rate of 8000 per sec. and ofduration about 2 as. These pulses are fed to a passive delay networkrepresented by block 2 having a large number of sections and having atotal Y delay of 125 as.. The output of the network 2 is fed back to lto stabilise the pulse frequency. Four outputs from network 2 a,- b, c,d Yare shown, these outputs will be in the form of 2 fis. pulses, bbeing 25 es. behind the input pulse at a, c 50 as. behind a and thepulses corresponding to respective other channels following at 25 as.intervals, so that pulses for channel d are us. behind a. The outputfrom I is also fed by path e to a device which converts eachpulse intotwo pulses to distinguish the pulseY train in the path from theremaining pulse trains at the receiver. The double pulse shown at f isused as the synchronising pulse at the receiver for synchronising thereceiver distributor to the transmitter distributor. The channel pulsetrain from tapping c of the network 2 is shown as being used for thecommunication channel and will be duration modulated by knownarrangementsindicated by block 4 the leading edge remaining unaffectedby the modulation.

The modulated pulse is then Vfed to the transmitter represented by block5 where it modulates the carrier wave which is radiated bythe aerial 5which may be an omni-directional one. The other channels are used asrequired. For instance the pulses of channel d are shown modulating anR. F. transmitter represented by block l so that the transmitterproduces pulses 'at 8000 P. P. S. repetition frequency. These pulsesfrom 1 are shown in Fig. 2 and designated' channel d. This pulsetrain'then' passes through a known switching device represented by block8 and is applied alternately to directive' antennae 9 and l0 in a dotdash rhythm, :for/'exampla'to atraves produce an approach course byoverlapping eld patterns.

At the receiver the pulses are received as a train of pulses andamplified and appear as D. C. pulses at the output of the main receiverrepresented by block I I.

The double synchronising pulse is selected by an arrangement representedby block I2 and produces a single pulse, as will be described inrelation to Figure 4. This pulse is used to control .a pulse generatorrepresented by block I3, e. g. a multivibrator the output of which,after shaping if necessary, is fed to a passive delay networkdistributor represented by block I4 from which, as in the transmitterselector pulses are obtained at tapping points a, b, c and d spaced 25its. apart; pulse a will be 23 its. behind the original synchronisingpulse at the output of receiver i and is used in known manner to makethe gating circuit represented by block I5 sensitive 2 tis. beforechannel a pulse arrives at the gating circuit. Selector pulse amaintains I5 sensitive until the received pulse of channel a has passedthrough and then closes the gate. The pulses of channel a passingthrough the gate I5 are fed to a pulse detector circuit represented byblock I5 and are used to obtain the necessary information derived fromsignal modulations applied at modulator Fig. l.

In a similar manner the other channels b, c and d are selected bysimilar gate circuits. Automatic volume control is obtained either fromthe synchronising pulse selector output from I2 as shown or from theoutput of the communication channel and after amplification in amplifierrepresented by block Il is used to maintain the receiver sensitivitysuitable for receiving the desired beacons. It will be seen that if thecraft iiies at the rear of the approach course beacon where the signalfor the approach course will be very weak that the sensitivity will notdepend on the approach course signals but on the pulses radiated fromthe omni-directional antenna 6 of Fig. l and any signals from theapproach course antennae will be so weak as to be ineifective orinaudible. It is only when the craft is in the approach sector that theapproach signals will be eifective or heard and in this sector therewill be no false courses.

Figure 4 shows one form of circuit which the pulse selector I2, Figure 3may take. The double synchronsing pulse is indicated at I8, there beingtwo microseconds between the two pulses. The rst pulse PI drives thegrid GI of an amplifier valve V positive, but grid G2 remains atnegative potential for 2 microseconds produced by a delay devicerepresented by block I9. The pulse Pl then drives G2 positive, but atthis instant grid GI is also positive due to the second pulse P2, sothat the valve V conducts and a pulse is produced which may be obtainedfrom a resistance 20 in the anode circuit, or alternatively in thecathode circuit of V.

In Figure 5 block 2l represents a radio frequency oscillator the outputof which is fed to a radio frequency amplifier represented by block 22,and a radio frequency amplier represented by block 23. A pulse generatorof pulses of rectangular wave form and of frequency 5000 pulses persecond is represented by block 24, and feeds into the amplifier andmodulator 22 the pulse modulated output of which is fed to aerials 25and 26 through the switching device 21 which feeds pulse energy to theaerials alternately for example in a dot-dash rhythm. The

CTI

switching device may be electronic, for example utilising gatingcircuits opened by pulses of rectangular wave form complementary orreversed with respect to each other. Such devices are well known andfurther details are not considered necessary. Alternatively, theswitching device 2T may be mechanical.

The radio frequency from 2| applied to ampli- Iier and modulator 23 ispulse modulated at a pulse repetition frequency of 8000 pulses persecond of rectangular wave form supplied from the generator representedby block 28. The pulse modulated carrier frequency output from 23 is fedto modulator represented by block 29 in which it is amplitude modulatedby, for example a speech wave from source represented by block 30.Alternatively the speech wave may be employed to time modulate thepulses generated by 28 in any known manner in the art of time modulatedpulses. These time modulated pulses--time phased or duration modulated,are then applied to modulate the radio frequency from 2l applied to 23.In any event the speech modulated pulse carrier wave from 23 or 29 isfed to energise the omni-directional aerial 3l to provide thecommunication channel.

Figure 7 shows schematically a receiving circuit for use with the beaconsystem of Figure 5. Y

In Figure 7 the receiver aerial is indicated by 32 and feeds a radiofrequency receiver of known form represented by block 33, the output ofwhich consists of D. C. pulses at 8,000 `and 5,000 pulses per second andthe pulses being approximately of 2 microseconds duration. These twotrains are separated by means of filters represented respectively byblocks 3d and 35. The output of 34 is represented in curve a, Figure 6,which shows the pulses of unequal amplitude during the dot and dashperiods, that is when the receiver is orf the course defined by theoverlapping patterns of aerials 25 and 26, Figure 5. The output of 34 isapplied to a course meter 35 of the form usually employed in approachpath systems which denne the desired paths or course by overlappingradiation patterns.

The output from filter 35 at 8,000 pulses per second is applied todetector or demodulator circuit represented by block 31. Thisdemodulator will be of any known type suited to the type of modulationemployed. The speech wave is obtained in the output 38 and fed to asuitable form of translation device. Curve b, Figure 6, shows the pulseoutput pulses of 35 as duration modulated.

As in the case of the receiver shown in Figure 3 automatic volumecontrol voltages are obtained from the output of detector 31 which isobtained from the omni-directional radiation of the beacon arrangementof Figure 5 and the control voltages are applied by conductor 39 tocontrol the receiver gain which is therefore adjusted according to thestrength of this omni-directional signal. As described in relation toFigures 1 to 4 false courses are eliminated by obtaining the automaticvolume control voltages from the omnidirectional signal.

Since the pulse repetition frequency is of the order of 8,000 pulses persecond and the pulse duration is two micro-seconda' the pulses are onlyon for 16/ 1to0 of the time and since the repetition frequencies of thetwo radiations are different the times during which the two sets ofpulses coincide is negligible, and no question of interference due tousing the same carrier frequency for both transmissions arises. Theaerials for the two transmissions, i. e., the approach path aerials andthe omni-directional aerial, can, therefore, be placed in the mostconvenient position for each.

It will be understood that all the items represented by blocks in theaccompanying drawings Y are Well known and any suitable type which willfulll the desired function of the item may be employed.

Also while reference has been made particularly to complementary signaltype of system it will be understood that the invention is equallyapplicable to other systems delining a path for a mobile radio receiverby two overlapping radiation patterns, for example, systems in which theradiation patterns are constantly radiated, i. e. not commutated, butare distinguished by distinctive modulations.

Further, particular reference has been made to navigational systems foruse by aircraft by Way of example only but it will be understood thatsuch systems can be used equally well for use with other mobilereceivers, for example receivers carried by marine craft.

What is claimed is:

1. A radio navigational system having a plurality kof radiating meansincluding a beacon radiator and an omnidirectional radiator, means forsupplying each of said radiating means with radiant energy pulses,including pulse generating means, and delay means for delaying saidpulses to distribute them to diierent output channels, including acommunication channel for transmitting intelligence signals, means forshaping pulses applied lto said Vomnidirectional radiator to providesynchronizing pulses, means for applying the energy from saidcommunication channel to said omnidirectional radiator,

and means for applying 'energyrfrom another of said channels to saidbeacon radiator.

2. A radio navigational system Vas claimed in claim 1, wherein eachchannel is provided with a gating circuit for the control thereof towhich pulses from said delay means arerespectively applied, whereby thepulse energy is permitted to pass to the channels.

3. A radio navigational system as claimed in claim 1, further comprisinga receiver unit, a distributor system at said receiver unit having meansresponsive to said synchronizing signals, said distributor systemserving to direct the pulses received to respective receiving apparatusaccording to the functions of the respective channels.

4. A radio navigational system according to claim 3, further comprisingautomatic volume control means at said receiver and means for derivingautomatic volume control voltage from pulses received from saidomnidirectional radiator.

CHARLES ERIC STRONG. LOUIS JOHN HEATON-ARMSTRONG.

REFERENCES CTED The following references are of record in the le of thispatent:

UNITED STATES PATENTS Number Name Date 2,199,634 Koch May 7, 19402,262,838 Deloraine et al Nov. 18, 1941 2,266,401 Reel/ES Dec. 16, 19412,372,620 Williams Mar. 27, 1945 2,400,127 McGuigan May 14, 19462,403,600 Holmes et al July 9, 1946 2,403,626 Wolff July 9 19462,407,199 l Wolff Sept. 3, 1946 2,433,381 Marchand Dec. 30, 1947

